The present invention is directed to an interlayer composition and devices formed therefrom.
For printed electronics, various metal nanoparticle inks including silver inks are broadly used in electronic device integrations. The printed conductor inks are often used as electrodes for various devices such as diodes and transistors. Therefore, in addition to high conductivity, the conductor ink should ideally provide a suitable interface for charge injection in device applications. Challenges often encountered include the ink wetting on the substrates which affects printing quality (printing line quality/resolution), uneven or not smooth surface of the substrate which makes the printing impossible, the loss of the ink conductivity and poor ink adhesion to substrates.
Previously Xerox® Corporation developed silver nanoparticles and inks which can be solution processed by ink jet printing for various electronic device applications. Xerox® Corporation has invented a nanosilver particle which is stabilized by an organoamine U.S. Pat. No. 8,765,025, which is hereby incorporated by reference herein in its entirety, describes a metal nanoparticle composition that includes an organic-stabilized metal nanoparticle and a solvent in which the solvent selected has the following Hansen solubility parameters: a dispersion parameter of about 16 MPa0.5, or more, and a sum of a polarity parameter and a hydrogen bonding parameter of about 8.0 MPa0.5 or less. U.S. Pat. No. 7,270,694, which is hereby incorporated by reference herein in its entirety, describes a process for preparing stabilized silver nanoparticles comprising reacting a silver compound with a reducing agent comprising a hydrazine compound by incrementally adding the silver compound to a first mixture comprising the reducing agent, a stabilizer comprising an organoamine, and a solvent.
U.S. patent application Ser. No. 13/866,704, which is hereby incorporated by reference herein in its entirety, describes stabilized metal-containing nanoparticles prepared by a first method comprising reacting a silver compound with a reducing agent comprising a hydrazine compound by incrementally adding the silver compound to a first mixture comprising the reducing agent, a stabilizer comprising an organoamine, and a solvent. U.S. patent application Ser. No. 14/188,284, which is hereby incorporated by reference herein in its entirety, describes conductive inks having a high silver content for gravure and flexographic printing and methods for producing such conductive inks.
Xerox® Corporation has developed flexographic and gravure inks based on silver nanoparticle technology. U.S. patent application Ser. No. 14/594,746, which is hereby incorporated by reference herein in its entirety, describes in the Abstract thereof a nanosilver ink composition including silver nanoparticles; polystyrene; and an ink vehicle. A process for preparing a nanosilver ink composition is described comprising combining silver nanoparticles; polystyrene; and an ink vehicle. A process for forming conductive features on a substrate using flexographic and gravure printing processes is described comprising providing a nanosilver ink composition comprising silver nanoparticles; polystyrene; and an ink vehicle; depositing the nanosilver ink composition onto a substrate to form deposited features; and heating the deposited features on the substrate to form conductive features on the substrate.
U.S. patent application Ser. No. 14/573,191, which is hereby incorporated by reference herein in its entirety, describes in the Abstract thereof a nanosilver ink composition including silver nanoparticles; a clay dispersion; and an ink vehicle. A process for forming conductive features on a substrate is described including providing a nanosilver ink composition comprising silver nanoparticles; a clay dispersion; and an ink vehicle; depositing the nanosilver ink composition onto a substrate to form deposited features; and heating the deposited features on the substrate to form conductive features on the substrate. Inks have been successfully formulated in non-polar solvents such as decalin and bicyclohexyl and successfully printed using inkjet printing technologies.
U.S. patent application Ser. No. 14/981,419, which is hereby incorporated by reference herein in its entirety, describes in the Abstract thereof an interlayer composition including an epoxy resin; a polyvinyl phenol; a poly(melamine-co-formaldehyde) polymer; a solvent; an optional surfactant and an optional catalyst. A device including a substrate; an interlayer disposed thereon; and conductive features; wherein the interlayer is formed from a composition comprising an epoxy resin; a polyvinyl phenol; a poly(melamine-co-formaldehyde) polymer; an optional surfactant and an optional catalyst. A process for forming conductive features on a substrate including depositing an interlayer onto a substrate; thermally curing the interlayer; depositing a conductive composition onto the interlayer to form deposited features; and annealing the deposited features to form conductive features.
U.S. patent application Ser. No. 15/099,937, which is hereby incorporated by reference herein in its entirety, describes in the Abstract thereof a composition formed from ingredients comprising: an epoxy; a polyvinyl phenol; a cross-linking agent; an epoxy silane; and a solvent. A printable medium and other devices made from the composition are also disclosed.
A thin-film transistor (TFT) is a special kind of field-effect transistor made by depositing thin films of an active semiconductor layer as well as the dielectric layer and metallic contacts over a supporting (but non-conducting) substrate. A common substrate is glass, because the primary application of TFTs is in liquid-crystal displays. This differs from the conventional transistor, where the semiconductor material typically is the substrate, such as a silicon wafer. Organic thin-film transistor (OTFT) technology involves the use of organic semiconducting compounds in electronic components. A thin film is a layer of material ranging from fractions of a nanometer (monolayer) to several micrometers in thickness.
In order to provide a high performance printed organic thin film transistor (OTFT), a controllable line width with a minimal line-to-line spacing is required for the OTFT source and drain electrode printing. In addition, the electric properties, such as charge-trapping and emission at the interface of the interlayer and a semiconductor, are of importance as they affect transistor performance.
Solution based all-additive printing processes enable low cost fabrication of electronic devices on a large area flexible substrate. These printing processes offer several advantages including fast prototyping with on-demand custom device; patterning devices at low temperature, and applying to a broad range of applications for electronic device manufacture.
Many of these printing processes use organic semiconductors. Organic thin-film transistors (OTFT) have low electron or hole mobility. Because of this low mobility, the desired device performance requires a large ratio of the thin-film transistor (TFT) channel width to channel length (W/L). In order to achieve a high transistor current during device on state, it is desired to make the channel length, which is the dimension of the gap between the source and drain electrodes, as small as possible. Shown in FIG. 1 is a cross-sectional view of a top-gate OTFT 10. The OTFT 10 includes a substrate 12 and thereupon an interlayer 14. Source electrode 16 and drain electrode 18 form a gap or channel 20 therebetween. Semiconductor layer 22 is disposed between the gap 20. Gate dielectric layer 24 is disposed upon the semiconductor layer 22. Gate electrode 26 is disposed upon the gate dielectric layer 24. A voltage applied to the gate electrode imposes an electric field 28 into the semiconductor channel, which accumulates or depletes charge carried in the channel. The back channel interface 30 is the interface between the semiconductor layer 22 and the interlayer 14. Since the semiconductor layer 22 is thin (typically 50 nanometers), the gate voltage has a strong field effect at the back channel interface 30. In an undesired situation, charges may be moved in and out from the interlayer 14 to the semiconductor 22, causing poor device performance in terms of slow subthreshold slope and higher off-state leakage current.
Solution processable conducting materials including silver nanoparticle inks play an important role in electronic device integrations. Silver nanoparticle inks can be easily dispersed in suitable solvents and used to fabricate various conducting features in electronic devices such as electrodes and electrical interconnectors by low-cost solution deposition and patterning techniques and especially by ink jet printing technologies.
The conductive features formed from metal nanoparticles such as silver nanoparticle inks on suitable substrates, including glasses and flexible plastic substrates, must have sufficient adhesion and mechanical robustness characteristics to enable proper electronic device fabrications and functions. However, one of the issues is that adhesion on certain substrates such as glasses and polyimide may not be adequate in some instances for robust device fabrications. The adhesion issue was tackled previously by addition of a small amount of polymeric materials including polyvinyl butyral (PVB) resin in silver conducting inks as an adhesion promoter. This approach is suitable for some applications. However, a potential disadvantage of this method is that the electrical conductivity of printed conductive features from such inks could, in some instances, be decreased significantly. Therefore, it is necessary to develop effective methods to improve adhesion and enable formation of devices with robust mechanical properties without sacrificing electric conductivity of metal nanoparticle inks used in electronic device applications.
Currently available compositions and methods are suitable for their intended purposes. However a need remains for improved electronic device compositions and methods. Further, a need remains for an improved method for providing sufficient adhesion and mechanical robustness characteristics while also maintaining desired electrical conductivity of the printed conductive features. Further, a need remains for an interlayer composition having the characteristics of film forming capability, adequate film adhesion, in embodiments, adequate film adhesion to glass substrates, ability to accept conductive ink, in embodiments silver ink, wherein a film formed from the interlayer allows desired adhesion of conductive ink to the film, non-polar solvent based silver ink wettability, and desired conductivity. In embodiments, what is desired is an interlayer composition providing a combination of these desired characteristics; that is, an interlayer composition that provides all of the following characteristics: film forming ability, film adhesion to glass, ink adhesion to film, non-polar solvent based ink wettability, and desired conductivity. Further, a need remains for a high performance printed organic thin film transistor (OTFT) and improved method for preparing same, providing a controllable line width with a minimal line-to-line spacing which is required for the OTFT source and drain electrode printing. In addition, a need remains for an improved device and process providing electric properties, such as charge-trapping and emission at the interface of the interlayer and a semiconductor. Further, a need remains to address the issue that organic thin-film transistors (OTFT) have low electron or hole mobility. Because of this low mobility, the desired device performance requires a large ratio of the thin-film transistor (TFT) channel width to channel length (W/L). In order to achieve a high transistor current during device on state, a need remains for improved devices and processes to make the channel length, which is the dimension of the gap between the source and drain electrodes, as small as possible.
The appropriate components and process aspects of the each of the foregoing U.S. patents and patent Publications may be selected for the present disclosure in embodiments thereof. Further, throughout this application, various publications, patents, and published patent applications are referred to by an identifying citation. The disclosures of the publications, patents, and published patent applications referenced in this application are hereby incorporated by reference into the present disclosure to more fully describe the state of the art to which this invention pertains.